Intermittency of Deformation and the Elastic Limit of an Icosahedral Virus under Compression

Viruses undergo mesoscopic morphological changes as they interact with host interfaces and in response to chemical cues. The dynamics of these changes, over the entire temporal range relevant to virus processes, are unclear. Here, we report on creep compliance experiments on a small icosahedral virus under uniaxial constant stress. We find that even at small stresses, well below the yielding point and generally thought to induce a Hookean response, strain continues to develop in time via sparse, randomly distributed, relatively rapid plastic events. The intermittent character of mechanical compliance only appears above a loading threshold, similar to situations encountered in granular flows and the plastic deformation of crystalline solids. The threshold load is much smaller for the empty capsids of the brome mosaic virus than for the wild-type virions. The difference highlights the involvement of RNA in stabilizing the assembly interface. Numerical simulations of spherical crystal deformation suggest intermittency is mediated by lattice defect dynamics and identify the type of compression-induced defect that nucleates the transition to plasticity.